We present the first results of a program to identify the unknown bright active galactic nuclei (AGN) in the ROSAT All Sky Survey Bright Source Catalog (RASS-BSC). We have used logC+0.4R as an alternative expression for log(f_X_/f_opt_), where C is X-ray count rate and R stands for R magnitude. Then a high X-ray-to-optical flux ratio criterion has been used to select an AGN sample with 165 unidentified X-ray sources for optical spectroscopy. Those 165 X-ray sources have been identified in the following classes: 115 emission line AGN (QSOs and Seyferts), 2 BL Lac objects and 4 BL Lac candidates, 22 clusters of galaxies, 12 Galactic stars and 10 objects remain unidentified. This represent a success rate of about 73% for detecting AGN using our selection criteria. Plausibility is based upon the optical classification and X-ray characteristics of the sources.
We present the ROSAT All-Sky Survey data in a 126 deg^2^ area in and around the CrA star forming region. With low-resolution spectroscopy of unidentified ROSAT sources we could find 19 new pre-main sequence stars, two of which are classical T Tauri stars, the others being weak-lined. The spectral types of these new T Tauri stars range from F7 to M6. The two new classical T Tauri stars are located towards two small cloud-lets outside of the main CrA cloud. They appear to be ~10 Myrs old, by comparing their location in the H-R diagram with isochrones for an assumed distance of 130 pc, the distance of the main CrA dark cloud. The new off-cloud weak-line T Tauri stars may have formed in similar cloudlets, which have dispersed recently. High-resolution spectra of our new T Tauri stars show that they have significantly more lithium absorption than zero-age main-sequence stars of the same spectral type, so that they are indeed young. From those spectra we also obtained rotational and radial velocities. For some stars we found the proper motion in published catalogs. The direction and velocity of the 3D space motion - south relative to the galactic plane - of the CrA T Tauri stars is consistent with the dark cloud being formed originally by a high-velocity cloud impact onto the galactic plane, which triggered the star formation in CrA. We also present VRIJHK photometry for most of the new T Tauri stars to derive their luminosities, ages, and masses.
We describe the ROSAT International X-ray/Optical Survey (RIXOS), a medium-sensitivity survey and optical identification of X-ray sources discovered in ROSAT high Galactic latitude fields (|b|>280) and observed with the Position Sensitive Proportional Counter (PSPC) detector. We presents a catalogue of the RIXOS sources and their optical identifications.
Table 2 gives the 5 GHz high resolution radio source properties for the 1861 Rosat-GreenBank (RGB) sources for which subarcsecond positions and core radio flux densities were obtained. After submission of this paper, we discovered a possible systematic position error in a very small subset of sources. In particular, the sources RGB J0131+005, RGB J0139+178, RGB J0143+129, RGB J0157+235A, RGB J0232+202, RGB J0233+024A, RGB J0243+171, RGB J0256+035, RGB J0303+059, RGB J0308+104, RGB J0312+243A, RGB J0312+242C, and RGB J0314+063 were all observed in our "c" epoch VLA runs and show large systematic offsets with respect to sources found in the NVSS survey. We re-examined these sources and found the position reported in the tables is accurate given our data, but that the noise on these fields before any CLEANing is abnormally high. We thank Dr. Alastair Edge for pointing out this discrepancy. Table 3 gives the 5 GHz radio source properties for the 436 Rosat-Green Bank (RGB) sources for which only low resolution data were obtained. Table 4 gives the 83 Rosat-Green Bank (RGB) sources for which no radio source greater than 5 sigma was observed in the follow-up VLA observations. These catalogs consist of radio- and X-ray-loud AGN selected from a correlation of the 1987 Green Bank radio catalog and the Rosat All-Sky Survey.
The ROSAT All-Sky Survey Bright Source Catalogue (RASS-BSC, revision 1RXS) is derived from the all-sky survey performed during the first half year (1990/91) of the ROSAT mission. 18,806 sources are catalogued (five sources were removed compared to the 18,811 sources of the 1996 version), down to a limiting ROSAT PSPC count-rate of 0.05cts/s in the 0.1-2.4keV energy band, with a detection likelihood of at least 15 and with at least 15 source photons. For 94% of the sources visual inspection confirmed the results of the standard processing with respect to existence and position; the remaining 6% were re-analysed and appropriately flagged. At a brightness limit of 0.1cts/s (8,547 sources) the catalogue represents a sky coverage of 92%. Broad band images are available for a subset of the flagged sources from http://www.rosat.mpe-garching.mpg.de/survey/rass-bsc . Questions or comments may be directed to <xray-info(at)mpe.mpg.de>
For the detailed statistical analysis of the X-ray emission of hot stars we selected all stars of spectral type O and B listed in the Yale Bright Star Catalogue and searched for them in the ROSAT All-Sky Survey. In this paper we describe the selection and preparation of the data and present a compilation of the derived X-ray data for a complete sample of bright OB stars.
The ROSAT All-Sky Survey Faint Source Catalogue (RASS-FSC) is derived from the all-sky survey performed during the ROSAT mission in the energy band 0.1-2.4 keV. 105,924 sources are catalogued and represent the faint extension to the RASS bright source catalogue (RASS-BSC, 1999A&A...349..389V, See Cat. <IX/10>). The sources have a detection likelihood of at least 7 and contain at least 6 source photons. (The likelihood of source detection is defined as L = -ln(1-P), with P = probability of source detection). For each source we provide the ROSAT name, the position in equatorial coordinates, the positional error, the source countrate and error, the background countrate, exposure time, date of observation, hardness-ratios HR1 and HR2 and errors, extent and likelihood of extent, and likelihood of detection. Questions or comments may be directed to xray-info(at)mpe.mpg.de
We present new spectra of dominant galaxies in X-ray-selected clusters of galaxies, which combine with our previously published spectra to form a sample of 256 dominant galaxies in 215 clusters. 177 of the clusters are members of the ROSAT Brightest Cluster Sample (BCS; Ebeling et al., 1998MNRAS.301..881E), and 17 have no previous measured redshift. This is the first paper in a series correlating the properties of brightest cluster galaxies and their host clusters in the radio, optical and X-ray wavebands.
The ROSAT Bright Survey (RBS, table "rosat.dat") aims to completely optically identify the 2072 brightest sources detected in the ROSAT all-sky survey (Cat. <IX/10>) at galactic latitudes |b|>30{deg} (excluding LMC, SMC, Virgo cluster), with countrate above 0.2s^-1^; this program is 99.5% complete, and a sub-sample of 931 sources with countrate above 0.2s^-1^ in the hard spectral band between 0.5 and 2.0keV is 100% identified. The total survey area comprises 20391{deg}^2^ at a flux limit of 2.4x10^-12^erg/cm^2^/s in the 0.5-2.0keV band. Tables 1 and 3 examine the "RHS" sub-sample of 66 bright point-like ROSAT survey sources with almost hard PSPC spectra (hardness ratio HR1>0.5) which could be nearly completely identified by low-resolution optical spectroscopy with the following breakdown into object classes: 31 Seyfert galaxies (20 Sy1), 22 BL Lac candidates, 5 clusters of galaxies, 1 cataclysmic variable, and 5 bright stars. Only one object remained unidentified and one X-ray source was a spurious detection.
The ROSAT Deep Survey in the Lockman Hole is the most sensitive X-ray survey performed to date, encompassing an exposure time of 207ksec with the PSPC and a total of 1.32Msec with the HRI aboard ROSAT. Here we present the complete catalogue of 50 X-ray sources with PSPC fluxes (0.5-2 keV) above 5.5x10^-15^erg/cm^2^/s.